Apparatus for making absolute two-demensional position measureme

Details Apparatus for making absolute two-demensional position measureme Apparatus for making absolute two-demensional position measureme

1992-03-12

1994-08-23

Willis, Davis L.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356356, 356358, 359 1, 359 15, 250572, 250237G, G01B 1102

Patent

active

053412117

DESCRIPTION:

BRIEF SUMMARY
STATE OF THE ART

The invention relates to an apparatus for making absolute two-dimensional measurements of the position of an object relative to a measuring arrangement.
German Patent Application DE-P 3,821,046 discloses a method of measuring travel and/or angles by opto-electronic means in which a first and a second optical beam are directed at predetermined angles onto the surface of an object to be measured and are diffracted on the surface at a common point of incidence. Both beams either have different frequencies or the frequency of the two beams changes simultaneously, with one of the beams being modulated in phase. The change in phase of the signal emitted by an optical sensor relative to a reference signal is evaluated. Diffraction takes place at the point of incidence of the two beams on the surface of the object to be measured because the surface always has a certain roughness which has the effect of an optical grating. The prior art method is able to perform an absolute position measurement if, at a certain measuring moment, for example at the beginning of the measurement, a reference position is defined. However, an absolute measurement of the position of the object to be measured relative to the measuring arrangement on the basis of the just compiled measured values is not possible.
It is the object of the invention to provide an apparatus for making two-dimensional measurements of the position of an object relative to a measuring arrangement so as to permit an absolute position measurement to be made from the just obtained measured values.


SUMMARY OF THE INVENTION

The above object is generally achieved according to the present invention by an apparatus for making absolute, two-dimensional measurements of the position of an object with reference to a measuring arrangement wherein an optical measuring wave is directed onto a surface of the object, with the surface being configured as a hologram and an optical reference wave is provided for interfering with the measuring wave diffracted by the hologram, an optical sensor arrangement comprising at least two sensors is provided for detecting the interfered-with waves, and a signal processing arrangement determines the position of the object from the output signals of the sensors and from a value stored in a memory.


ADVANTAGES OF THE INVENTION

The basic apparatus according to the invention as described above exhibits very high resolution at relatively little expense. The configuration of at least one surface of the object to be measured as a hologram permits the accommodation of a great information density which is evaluated by the simply configured optical measuring arrangement.
The information contained in the hologram is evaluated in that a measuring wave is directed onto the hologram and a reference wave is provided to interfere with the measuring wave diffracted by the hologram. The interfered-with waves are picked up by a sensor arrangement including at least two sensors whose output signals are fed to a signal processing arrangement which determines from these signals and from values stored in a memory the absolute, two-dimensional position of the object with reference to the measuring arrangement.
According to a first embodiment of the apparatus according to the invention the signal processing arrangement determines the absolute position from the sensor output signals which are proportional to the intensity of the interfered-with waves, for example by difference or quotient formation from the signals emitted by the at least two sensors. The significant advantage of this embodiment is the simple configuration of the optical arrangement because the measuring wave and the reference wave can both have the same frequency.
In a second embodiment it is provided that the signal processing arrangement determines the absolute position from the phase relationships between the output signals emitted by the at least two sensors. In this embodiment it is necessary that a phase or frequency modulation occurs between the measuring wave and the refe

REFERENCES:
patent: 4930895 (1990-06-01), Nishimura et al.
patent: 5141317 (1992-08-01), Bollhagen et al.

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